A tailor welded blank (TWB) combines a plurality of different metallic materials into a welded blank so that the best properties of the materials are located precisely where they are needed. The introduction of the TWB owes to the development in computerized structural analysis. As this new blank material is highly beneficial in reducing the weight of the structure while ensuring the required mechanical strength, the use of this material for automotive bodies has advanced significantly over the past years with the aim of reducing weight and improving the fuel economy.
Typically, a TWB is prepared by welding a plurality of individual blank pieces having different thicknesses and/or mechanical properties into a single blank, and the single blank or the TWB is stamp formed into a prescribed shape. See Japanese patent laid open publication No. 8-243770 (patent document 1), for instance.
The technology disclosed in patent document 1 is directed to the use a TWB to an outer panel of a vehicle body side structure. In particular, a plurality blank pieces are laser welded into a single C-shaped blank, and an additional blank piece forming a center pillar is spot welded to the C-shaped blank so as to form a frame structure defining a door opening. Therefore, provided that the spot welded portions are avoided from being significantly drawn during the subsequent stamp forming process, the frame structure can be formed as a single blank without requiring any significant precision during the welding of the individual blank pieces. This prior art has the advantage of simplifying the welding process in preparing a TWB, but imposes some restriction in the stamp forming process.
As a vehicle body side structure requires a particularly high mechanical strength in selected parts thereof, there is a high gain in applying the TWB approach to a vehicle body side structure. However, there are some problems that need to be overcome when applying the TWB approach to a vehicle body side structure. As a vehicle body side structure requires a relatively large blank, a corresponding large forming pressure is required in the stamp forming process. It is also desired that the welding process required for forming a TWB does not require any undue welding precision.